1. Field of the Invention
The present invention relates to microwave ovens and more specifically to the construction of the cooking cavity and cabinet for a microwave oven.
2. Description of the Prior Art
Microwave ovens designed for home and commercial use in heating food items require a carefully designed and constructed cabinet structure enclosing the cooking cavity in order to ensure uniform heating throughout the cavity and to avoid leakage of microwave radiation. Since the operator of such an oven must have easy access to the interior of the cavity, a door is generally provided on the front side of the cavity. To obtain a good door seal, the cabinetry around the front of the cavity must extend vertically and horizontally to provide a flat overlapping area for the door seal. Thus, the front cabinet panel is larger than the cavity opening and needs to define a front surface having a sufficient dimension around the cavity opening for a door seal to work properly.
In previous microwave cavity constructions, the panels defining the cooking cavity are generally joined by spot welding techniques in that a metal-to-metal contact is required to prevent the transmission and leakage of microwave radiation out of the cavity enclosure. Also, a smooth front surface surrounding the door is required for aesthetic purposes and thus many types of fasteners such as rivets and screws are not acceptable. The use of spot welds in microwave cavity construction causes the associated panels to move during fabrication due to the heating and cooling of the metal when the welds are formed. When individual side panels are utilized, the movement of the panels does not effect the resulting cabinet structure so much as when the panels are fabricated in a prejoined manner, such as by folding a large metal sheet.
Spot welding does create other problems in that it is a somewhat unreliable process which requires an increased number of individual spot welds to be factored into the design of the cabinetry construction to account for an occasional bad weld. Also, spot welds look unsightly on the front panel of the microwave oven causing that portion of the cabinet to be reworked by grinding or a similar operation prior to painting of the metal surface. Further, as described above, spot welding can distort parts locally causing puckers which also have to be mechanically removed, such as by grinding or by covering with an additional plate.
Some microwave cabinetry constructions utilize a metal crimping arrangement to attach adjacent panels, but because of the design of the crimps utilized, the minimum number of parts used to form the cooking cavity have been three. One reason for this is that because the entire front frame must have the ability to move in relation to the cavity to form the crimp. A fully crimped cavity design is now known which requires at least four plates or panel members. The plates are crimped together to form the cooking cavity. This construction further requires that a bottom panel and rear panel be added to form the oven cabinet.
Crimping has an additional advantage over spot welding in that it consumes much less energy since crimping only requires die pressure as opposed to the high voltage requirements for spot welding.